(i) Field of the Invention
This invention relates to a water soluble powdered formulations of reagent mixtures containing water-insoluble reagents and a process for their preparation.
(ii) Description of the Prior Art
Benzidine which has traditionally been used as a horseradish peroxidase HRP! substrate is now known to be a carcinogen. Consequently, 3,3',5,5'-tetramethylbenzidine hereinafter referred to as TMB! is now being used more often instead of benzidine.
Water-insoluble reagents often need to be homogenized or solubilized in aqueous solutions in chemical or enzymic analyses in order for required reaction to take place. A common strategy to achieve this condition is first to dissolve the reagents in water-miscible solvents, e.g., ethanol, p-dioxane, dimethylformamide, and dimethylsulfoxide, and then to mix the reagent solution with an aqueous medium.
The above-referred-to TMB is an example of a chromogenic substrate of HRP. A soluble TMB substrate system is used to detect HRP enzyme activity by measuring the intensity of a soluble blue or a yellow color product (after the addition of sulfuric or phosphoric acid to the blue product) as found in enzyme immunoassay EIA!. An insoluble TMB substrate system is used to detect HRP enzyme activity by the intensity of blue colored insoluble end product found on the surface of a membrane, in membrane enzyme immunoassay, or cloth, in cloth-based enzyme immunoassay CEIA!. These TMB systems are extremely sensitive and are the presently most commonly used reagents for detecting peroxidase labels in various EIAs. HRP is one of the most widely used enzyme labels in EIA and is at least 10-fold less expensive than alkaline phosphatase, another popular EIA enzyme. HRP catalyses the transfer of hydrogen from TMB to hydrogen peroxide (H.sub.2 O.sub.2) to produce water and oxidized TMB, which becomes blue. TMB provides a highly sensitive assay of HRP as compared to other HRP substrates. Moreover, TMB is non-carcinogenic, unlike other HRP substrates, (e.g., benzidine). However, TMB is poorly soluble in water. To obtain a TMB suspension, TMB is first dissolved in water-miscible solvents, e.g., ethanol, dimethylformamide or dimethylsulfoxide before mixing. Alternatively, salts of TMB with strong acids (e.g., HCl) may be solubilized in a buffer without the aid of the solvent. However, in either case, the resulting TMB suspension is unstable, TMB being crystallized out gradually.
There are several commercial liquid formulations of TMB/HRP substrate systems in which TMB is stabilized by use of dimethylformamide, dimethylsulfoxide or proprietary surfactants or reagents. These two forms of TMB liquid formulations which are presently commercially available are "soluble" TMB reagent and "insoluble" TMB reagent. HRP action converts "soluble" TMB reagent into "soluble" blue colored products and converts "insoluble" TMB reagent into "insoluble" blue precipitate or stain. "Soluble" TMB reagent is useful for calorimetric determination of HRP as used in quantitative enzyme immunoassay based on microplates or macroporous hydrophobic cloth "segments".
A soluble TMB substrate system is used to detect HRP enzyme activity by measuring the intensity of a soluble blue or a yellow color product (after the addition of sulfuric or phosphoric acid to the blue product) found in EIA. An insoluble TMB substrate system is used to detect HRP enzyme activity by the intensity of blue colored insoluble end product found on the surface of a membrane or a cloth in membrane EIA or cloth in CEIA. These TMB systems are extremely sensitive and are the most commonly used reagents for detecting peroxidase labels in various enzyme immunoassays.
Thus, as noted above, "soluble" TMB reagent may be used for EIA for antigen on antibody-coated cloth "segment". One example of such EIA involves coating of cloth segment with an antibody, capturing of sample antigens, reaction with antibody-HRP conjugate, soluble color development with "soluble" TMB reagent, and calorimetric determination.
"Insoluble" TMB reagent is useful for visual observation of HRP action as used in qualitative EIA which visually compares the color intensity of the blue stains shown by multiple samples applied (or transferred) onto a "sheet" of cloth or membrane.
"Insoluble" TMB reagent is equally useful for dot blot assay of antigens on a sheet of membrane (e.g., nitrocellulose membrane) in the following procedure: direct spotting of sample antigens on "uncoated" membrane, blocking of the membrane with blocking proteins (e.g., non-fat dry milk), and detection of antigens by antibody-HRP as blue-stained spots. "Insoluble" TMB reagent moreover is equally useful for "Western blot" (a popular molecular biology technique) in the following procedure: fractionation of protein by gel electrophoresis, transfer of fractionated proteins to a membrane (e.g., nitrocellulose or polyvinylidene difluoride membrane), reaction with antibody-HRP conjugate, and detection of protein antigens as blue-stained bands.
TMB substrate systems can also be used to determine hemoglobin since hemoglobin, like HRP, catalyses the oxidation of TMB to colored product in the presence of H.sub.2 O.sub.2. The level of plasma hemoglobin is measured by TMB reagents to monitor hemolytic conditions.
Commercially-available TMB substrate systems are all in liquid form, which adds weight and bulkiness, making packaging expensive. Furthermore, they are usually shipped via air because of their instability. Thus, packaging and shipment of the liquid formulations are not only costly to the users but also environmentally unfriendly. In addition, the TMB liquid formulations are recommended for refrigerated storage, occupying a large space in a laboratory refrigerator. Prior to use, the liquid formulations need to be equilibrated to HRP assay temperatures.
Accordingly, it is desirable to provide TMB (both "soluble" and "insoluble" TMB) in compact powder forms which are stable at ambient temperatures and which are readily and easily soluble in aqueous media. Such powder formulations not only reduce package size and shipment costs but also permit their prolonged use in fields lacking refrigeration (required for liquid formulations).
The art is replete with patents which provide for the water solubilization of water-insoluble reagents. The traditional manner of dissolving water insoluble reagents, (as noted hereinabove), has been to use non-aqueous solvents. In fact, TMB has been dissolved in the past in such non-aqueous solvents, e.g., in ethanol.
U.S. Pat. No. 4,503,143, patented Mar. 5, 1985, by B. Gerber et al, provided an enzyme immunoassay with two-part solution of TMB as a chromogen. The patentee provided an activated solution containing organic or inorganic acid salts of TMB (TMB solution), particularly an activated solution containing sulfated TMB (TMB-S). The activated solutions contained the TMB component, solvent, buffer, and hydrogen peroxide. A preferred buffer which enhanced the stability of the activated solutions was composed of citrate phosphate dissolved in water, having a pH of about 5.0. When the activated solution contained tetramethylbenzidine, the preferred solvent was methanol. However, an activated solution containing, instead, a water-soluble salt of tetramethylbenzidine, e.g., sulfated tetramethylbenzidine, had an advantage in that it avoided the need for solvents other than water.
Thus, the patentee merely provided activated aqueous or alcoholic/aqueous solutions containing TMB for immunoassay purposes.
U.S. Pat. No. 4,596,770, patented Jun. 24, 1986, by M. Parham et al, (and its corresponding Canadian Patent No. 1,246,443 patented Dec. 13, 1988), provided for the assay of peroxidase enzyme activity. The patentee taught the use of aqueous N-methylpyrrolidone as a solvent for a substrate containing tetraalkylbenzidine chromogen and a peroxide in determining peroxidase enzyme activity provides increased stability of the substrate solution and decreased substrate drift in carrying out enzyme immunoassays or enzyme-linked immunosorbent assays. By this patent it was taught provided an enzyme immunoassay or enzyme-linked immunosorbent assay in which 3,3',5,5'-tetraalkylbenzidine chromogen or an acid salt thereof and a peroxide are reacted with a peroxidase in an aqueous buffered substrate medium. The chromogen or acid salt was provided in solution in an aqueous medium containing 5 to 20% by volume of N-methylpyrrolidone (NMP).
Thus, the patentee merely provided a different solvent for an aqueous solution of TMB with low background.
U.S. Pat. No. 4,615,972, patented Oct. 7, 1986, by J. J. Gallacher, (and its corresponding Canadian Patent No. 1,231,633 patented Jan. 19, 1988), provided for the stabilization of indicators for detecting enzyme activity. The patentee provided a stabilized indicator powder for use in assays to detect the presence of peroxidase or other peroxidatively active substances. An indicator was combined with a stabilizer substance to produce a stabilized indicator powder. Preferred stabilizers were said to be solid water soluble polymers. To prepare the stabilized indicator powder, an indicator was mixed with a water-soluble polymer, e.g., polyethylene glycol, polyethyleneoxide or polyvinylpyrrolidone and derivatives thereof, followed by grinding the mixture. To prepare the stabilized indicator powder, the two compounds were first mixed with a paddle and then ground together, either with a mortar and pestle or in a ball mill for thirty minutes in the cold (i.e., at a temperature of about 4.degree. to 8.degree. C.). The aqueous medium into which the stabilized powdered reagent was dissolved may be either pure water or a previously prepared solution.
Thus, this patent provided a cold fusion technique for mixing the polymer with the indicator.
U.S. Pat. Nos. 5,006,461, patented Apr. 9, 1991, and 5,013,646 patented May 7, 1991, by J. E. Woiszwillo, provided a solvent system for use in increasing the solubility of TMB. The solvent system included, as a solvent, DMF, methanol, or DMSO with povidone, 1-ethyl-2-pyrrolidone polymers. The solution could be mixed directly into an aqueous buffer without precipitating the TMB being used to obtain the preferred viscosity.
Thus, this patent merely provided a new solvent system for TMB.
U.S. Pat. No. 5,024,935, patented Jun. 18, 1991, by G. J. McClune et al, (and its corresponding Canadian Patent No. 1,321,045 patented Aug. 10, 1993), provided a dye-providing composition, a diagnostic test kit, and their use in a method for ligand determination using a peroxidase labelled-receptor. The patentee taught that such a dye-providing composition comprised an aqueous solution of a water-soluble or water-dispersible polymer, e.g., a vinylpyrrolidone polymer, and an imidazole leuco dye capable of providing a dye in the presence of hydrogen peroxide and a peroxidative substance.
Thus, this patentee merely provided a stabilizer, e.g., vinylpyrrolidone, for an aqueous solution of an imidazole leuco dye.
U.S. Pat. No. 5,047,318, patented Sep. 10, 1991, by B. A. Snyder et al, provided a dye-providing composition is useful in various diagnostic assays wherein a peroxidase-labelled specific binding species is used. This composition is substantially free of peroxidase and such labelled species, and comprises an imidazole leuco dye and 4'-hydroxyacetanilide present in an amount up to about 2.5 m molar. This composition can be included as part of a diagnostic test kit.
The composition is provided in a water-soluble or water-dispersible polymer selected from the group consisting of vinylpyrrolidone polymers, acrylamide polymers, acrylic and methacrylic acid polymers, polyethylene glycols and polyamines.
Thus, the patent merely provided a solvent for the leuco dye.
U.S. Pat. No. 5,176,999, patented Jan. 5, 1993, by G. J. McClune et al, (and its corresponding published Canadian Patent Application No. 2,028,175, as well as U.S. Pat. No. 5,366,864, patented Nov. 22, 1994 by G. J. McClune), provided a buffered wash composition, insolubilizing compositions, test kits and method of use. The patented buffered aqueous composition included a dye-providing composition, a buffer and an organic solvent having a certain molecular weight and water-solubility. The wash composition also included one or more water-soluble organic solvents having a molecular weight of from about 40 to about 100. Particularly useful solvents included the lower alcohols, e.g., ethanol, n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol and others known to one skilled in the art. Other useful solvents included acetonitrile, ketones, e.g., acetone and methyl ethyl ketone, and ethers, e.g., tetrahydrofuran and 1,4-dioxane. The preferred solvents were the lower alcohols, with sec-butanol being most preferred.
Thus, this patent merely taught the use of another solvent system for an aqueous solution of a benzidine.
U.S. Pat. No. 5,238,817, patented Aug. 24th, 1993, by M. N. Bobrow et al, provided a chromogenic substrate for improving detection in a peroxidase-based assay. The patentee taught that such a substrate for detecting peroxidase activity in a peroxidase-based assay included a substantially aqueous solution of at least a 1-naphthol derivative and tetramethylbenzidine.
Thus, this patentee merely provided a stabilizer, i.e., a 1-naphthol derivative, for an aqueous solution of TMB.
Canadian Patent No. 1,218,596, patented Mar. 3, 1987, by N. Kameda, provided a competitive immunofluorescence assay and test kit. In that patent, the reagents that were incubated with the sample suspected of containing antigen to form immune complexes, were (1) fluorescent-labelled antigen, (2) anti-antigen antibody, (3) antibody against the anti-antigen antibody, and (4) a non-fluorescent non-light-scattering immunoprecipitant. Compounds that were conventionally used to precipitate proteins and that had the required non-fluorogenic properties may be used. Examples of such materials included polyethylene glycol having a molecular weight in the range of about 3,000 to about 12,000, preferably about 4,000 to 10,000, and inorganic salts, e.g., ammonium sulfate. Polyethylene glycol was a preferred immunoprecipitant.
Thus, this patentee merely taught the use of polyethylene glycol as an immunoprecipitant, and not as a solvent.
Canadian Patent No. 1,277,895, patented Dec. 18, 1990, by M. J. Powell et al, provided assay reagents. The patentee taught that the peroxidase activity of a buffered aqueous solution containing a peroxidase or a peroxidase conjugate, and TMB as a chromogen could be stabilized by the use of a particular member of the family of cyclic oligosaccharides known as cyclodextrins. The patentee provided a TMB peroxidase-substrate reagent consisting of an aqueous solution comprising TMB and .beta.-cyclodextrin in solution. The .beta.-cyclodextrin acted to solubilize the otherwise sparingly soluble TMB.
Thus, the patentee merely taught a new carrier containing .beta.-cyclodextrin for an aqueous solution of TMB.
Canadian Patent No. 1,281,644, patented Mar. 19, 1991, by J. N. Eikenberry, provided a water-soluble composition comprising a peroxidase-labelled ligand analog and a water-soluble binder composition composed of at least about 50 percent, by weight, of poly(vinyl alcohol).
Thus, this patentee merely taught that an aqueous solution of a peroxidase labelled ligand can be stabilized by including therein at least 50% by weight of poly(vinyl)-alcohol.
Canadian Patent No. 1,286,986, patented Jul. 30, 1991, by W. Bloch et al, provided comprising a complex of a polymeric anion and a meriquinone of a benzidine compound, e.g., TMB. The reaction medium was aqueous to permit measurement of oxidative activity. However, the medium may also contain an organic co-solvent to control the solubilities of both the benzidine or substituted benzidine reactant and the meriquinone product. Preferred co-solvents, using horseradish peroxidase as catalyst, included iso-propyl alcohol, ethyl alcohol and dimethyl sulfoxide.
Thus, this patentee merely provided a solvent to provide an aqueous solution of a complex of a polymeric anion and a meriquinone of TMB.
Canadian Patent No. 1,290,661, patented Oct. 15, 1991, by I. A. Ismail et al, provided a stable composition from the determination of peroxidatively active substances. The stable test composition was 1,4-diisopropylbenzene dihydroperoxide and a benzidine indicator. The composition preferably provided TMB as the indicator and an organic solvent, e.g., ethanol, methoxypropanol and dimethylformamide, to dissolve the TMB.
Thus, this patentee merely provided a novel solvent for a TMB solution.